Turbine blade rings and methods of assembly



Nov. 29, 1960 B. -r. G. BISHOP ,96

TURBINE BLADE RINGS AND METHODS OF ASSEMBLY Filed Jan. 28, 1957 2 Sheets-Sheet 1 F/GZ.

INVENTQQ Bnsu. T. G. Bmnop JPM v an i 5 HTTORNEYS Nov. 29, 1960 B. 'r. e. BISHOP 2,962,259

- TURBINE BLADE RINGS AND mamons 0F ASSEMBLY Filed Jan. 28,' 1957 2 Sheets-Sheet 2 "lay/I- INVENTOIZ Bnsu. T. e. B|SHOP United States Patent TURBINE BLADE RINGS AND METHODS OF ASSEMBLY Basil T. G. Bishop, London, England, assignor to D. Napier & Son Limited, London, England, a company of Great Britain Filed Jan. 28, 1957, Ser. No. 636,729

Claims priority, application Great Britain Feb. 3, 1956 1 Claim. (Cl. 2533-77) This invention relates to turbine blade rings.

A problem that is frequently encountered in turbines is that of blade vibration and various proposals have been made either for preventing vibration or for reducing its harmful effects. One such proposal has been to lace the blades together by means of a wire ring passing through holes in the aerofoil portions of all the blades. When the turbine rotor is rotating at high speed the centrifugal force acting on the unsupported sections of the Wire between the blades presses the wire outwardly and may have the effect of bowing these unsupported sections outwardly between the blades. The wire therefore exerts frictional restraint against lateral flutter or transverse vibration of the blades, and is assisted in this by the said bowing out effect. One disadvantage of this arrangement is that the wire is disposed in the gas stream, which not only subjects the wire to high temperatures but may also "ice each wire, and it is desirable for the wire to be reasonably flexible so that the aforementioned bowing out effect will occur and to ensure that the wire will touch every blade through which it passes. It has been found that for a wire of given mass per unit length adequate flexibility can be achieved by making the (or each) wire in two separate interfere to some extent with the flow pattern of the gas stream passing through the blade channels.

In a turbine blade ring according to the present invention individual blades each comprising an aerofoil portion, a platform portion and a root portion are laced together by wire lacing passing through the platform portions.

An advantage of the invention is that the wire lacing is no longer located in the gas stream so that the aforementioned disadvantages are avoided. Nevertheless, the lacing still has the effect of reducing blade vibration by restricting transverse movements of the platform portions and hence of the blades as a whole.

In one form of the invention the wire lacing comprises at least one wire ring constituted by a single wire, or by a plurality of separate wire segments arranged end to end in the form of a ring, threaded through holes in the platform portions of the blade in the blade ring and with enlarged or deformed portions in the wire or wire segments of such size that they will not pass through the said holes. Assembly of the blade ring is facilitated by providing a plurality of wire segments instead of a single wire, while the enlarged or deformed portions prevent the wire or wires from being pulled out of the holes by centrifugal force.

In another form of the invention the lacing comprises several short lengths of wire each of which passes through holes in two adjacent platform portions, each blade being laced by at least one such Wire to the adjacent blade on one side and by at least one other such wire to the adjacent blade on the other side. Preferably, each end of each of the said short lengths of wire lies adjacent to an imperforate portion of a blade platform, which limits endwise movements of the short lengths of wire. Assembly of the blade ring is facilitated if the short lengths of wire are disposed obliquely with their axes inclined to the circumferential direction.

The vibration damping effect of the wire depends both upon its mass per unit length and its flexibility. Strength considerations, having regard to the high centrifugal forces involved, place an upper limit upon the mass of longitudinal sections which fit together toconstitute a wire of the desired external contour.

There is a growing tendency to make turbine blades of sheet or other thin metal and where the invention is applied to blades in which the platform portion is formed of thin metal it is desirable that the (or each) hole in the platform portion through which a wire passes should be reinforced by an inserted ferrule so that the wire does not rub directly against the thin metal and cause undue wear.

The invention may be performed in various ways and certain forms of turbine blade ring embodying the invention will now be described by way of example with reference to the accompanying drawings, in which:

Figure 1 is -a fragmentary front view of a turbine blade ring embodying the invention;

Figure 2 is a cross section of the lacing wire used in Figure 1, on an enlarged scale;

Figure 3 shows one method of anchoring the lacing wire;

Figure 4 shows another way of anchoring the lacing wire;

Figure 5 is a front view of a lacing wire ring made up of separate segments;

Figure 6 is a sectional developed plan view showing the application of the invention to thin metal blades; and

Figure 7 is a sectional developed plan view showing another method of lacing using a plurality of short lacing wires.

The turbine blade ring shown in Figure 1 comprises a ring of turbine blades 10 mounted around a turbine rotor disc 11. Each blade comprises an aerofoil portion 12, a platform portion 13 and a root portion 14. The platform portions 13 constitute a transition zone between the aerofoil portions 12 and the root portions 14, providing a smooth inner boundary to the blade channels which are defined between the aerofoil portions 12 of adjacent blades and at the same time providing a shield to prevent the hot gases which pass through these blade channels from coming directly into contact with the highly stressed rotor disc 11. The platform portion consists of a transverse front wall 30, a transverse rear wall 31, and at least one web 19 extending from said front wall to said rear wall. Thus the platform portion is of approximately the shape of a letter I in cross-section, which provides adequate rigidity against torsional vibration. In order to prevent transverse vibration of the blades, holes are drilled in the webs 19 of the platform portions 13 and a wire ring 15 is threaded through these holes. As shown in Figure 2, this ring is made in two parts 15A and 15B in order to increase its flexibility without increasing its mass per unit length.

In order to prevent the wire from being dragged out by centrifugal force in the form of a loop between two adjacent blades it is necessary to anchor the wire. One way of doing this is shown in Figure 3. In this case the wire is a single wire ring, its two ends 16 and 17 terminating in a space 18 between the webs 19A and 19B of the platform portions of two adjacent blades 10A and 10B.

To assemble the blade ring, the blades are threaded on to the wire 15, the blades 10A and 10B being held far enough apart to permit heads to be formed on to the two ends 16 and 17 of the wire as illustrated. The blades are then placed in a jig in the positions which they will occupy in the blade ring, and the turbine disc 11 is applied to them endwise so that all the root portions 14 enter their appropriate grooves in the rotor simultaneously.

Instead of, or in addition to, providing heads at the ends of the wire, the wire may be deformed at other places, for instance by squeezing it to form depressions 21 as shown in Figure 4, the wire bulging out laterally in the vicinity of these depressions. These depressions would be made at or near the centre of the wire, the blades being thereafter threaded on from each end.

Instead of having a single lacing wire, this wire could be sub-divided into several different segments 15C, 15D and so on, as shown in Figure 5, each of these segments being anchored in one or other of the previously mentioned ways.

In the case of a thin metal blade there would be a risk of excessive wear at the edges of the holes through the thin metal parts of the platform portions if precautions are not taken to prevent this. Such precautions may comprise inserting ferrulses 22 into the holes in the webs 33 and parts 23 of the platform portions as shown in Figure 6. Each ferrule has a central portion 24 of reduced diameter which fits snugly on the wire 25. The ferrules are Welded or brazed in place in the platform portions. The ends of the wire 25 are provided with heads 16A and 17A, corresponding to the heads 16 and 17, respectively, shown in Figure 3. The wire may be a ring made of a single length of wire or it may be segmental as shown in Figure 5.

'In the construction shown in Figure 7 of the web 26A, 268 etc. in the platform portion of each blade has two oblique holes drilled in it, the front hole in one web (e.g. 26C) being in alignment with the rear hole in the adjacent web 26B, and so on. The blades are laced together with short lengths of wire. Thus the blade 27C is laced to the blade 2713 by a short length of wire 28C which passes through the forward hole in the Web 26C and through the rear hole in the web 26B. The blade 27C is also laced close together in a jig into their final positions and moving the rotor disc endwise on to the root portions in the manner hereinbefore indicated. This method of assembly is facilitated by the oblique disposition of the Wires 28C, 28D etc.

The invention is applicable to axial flow compressors as well as to turbines, and accordingly the word turbine" is used herein in a broad sense as embracing both turbines proper and axial flow compressors.

What I claim as my invention and desire to secure by Letters Patent is:

A turbine blade ring comprising a rotor, a ring of individual blades mounted on said rotor each of said blades comprising an aerofoil portion, a root portion engaging said rotor, a platform portion intermediate between said aerofoil portion and ,said root portion, said platform portion having a transverse front wall, a transverse rear wall, at least one web extending from said front wall to said rear wall, and a reinforcing ferrule passing transversely through said web between said front and rear walls, and wire lacing passing through said ferrules in said webs of said blades and having unsupported portions between adjacent webs to damp transverse vibrations of said blades, said wire lacing comprising at least one wire ring constituted by a single length of wire threaded through said ferrules in said platform portions, said length of wire having enlarged portions of such size that they will not pass through said ferrules.

References Cited in the file of this patent UNITED STATES PATENTS 791,735 Wagenhorst June 6, 1905 1,017,467 Rice Feb. 13, 1912 1,542,402 Meissner June 16, 1925 2,141,401 Martinka Dec. 27, 1938 2,660,400 Grifiith Nov. 24, 1953 2,771 ,267 Weymouth Nov. 20, 1956 FOREIGN PATENTS 244,518 Great Britain Dec. 16, 1925 393,333 Germany Apr. 1, 1924 430,429 Germany June 18, 1926 587,588 Great Britain Apr. 30, 1947 685,110 France Mar. 25, 1930 910,154 France Jan. 21, 1946 

